Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$82.63	9.255%	$90.2774	$90.28	$90.30	$90.30
Purchase #2	$144.77	4.106%	$150.7143	$150.71	$150.70	$150.70
Purchase #3	$203.84	13.137%	$230.6185	$230.62	$230.60	$230.60
Purchase #4	$206.38	8.294%	$223.4972	$223.50	$223.50	$223.50
Purchase #5	$232.41	11.229%	$258.5073	$258.51	$258.50	$258.50
Purchase #6	$76.55	5.342%	$80.6393	$80.64	$80.65	$80.60
Purchase #7	$54.65	4.521%	$57.1207	$57.12	$57.10	$57.10
7 purchase totals =	$1,001.23		$1,091.3747	$1,091.38	$1,091.35	$1,091.30